In short<<<, have them find why the turbo is starved for oil and getting killed.
Long Version:
In my humble opinion the turbo charger replacements are due to a oil related issue inside your motor. Replacing the turbo without further explanation 3 times means there definitely is a problem. I am not familiar with the 2.5L used in the Forester as its unique in some ways to the Forester/Baja turbo only. It was not used till 2006 in the popular WRX and has very few issues there but they likely ironed them out.
Maybe visit a Subaru Forester forum and look at the common issues that occur with turbo Foresters of your year 2004/2005? For example my wife’s turbo Legacy in 2005 (different setup) that puts out 250HP instead of 212 HP like yours has an issue that DESTROYS the turbo.
Subaru decided to put a small fine mesh screen at the oil inlet line the 2005 Legacy/Outback turbo. This screen with negligent oil changes or time builds up with the debris and finally grenades the turbo. There have been cases where the turbo charger was replaced and talked about on this board and on another one where the mechanic’s/dealer did not replace or remove(Subaru 2006 design) this screen and the 2nd turbo suffered the same fate.
Here is a link that possibly can related to your issues:
[ur]Potential Subaru Turbo Oil Starvation Issues - NASIOC